This invention relates to signal processing apparatus and more particularly to a circuit for alternating successive simultaneous service requests applied to a multi-channel priority circuit.
A data processing device operating with more than one user device generally requires a priority circuit to determine which of the several user ports will be served next. There are two types of priority circuits. One operates on the preassigned priority basis in which requests for service are given different weights or priorities and are answered or served in accordance with that predetermination. In the other type of priority circuit, attempt is made to give all requests equal service. This invention is concerned with the latter type of priority circuit.
In the equal-priority circuit, request signals at the several input or request ports propagate through the circuit to the service or answering ports in a random or "free race" manner. The difficulty with the technique occurs when there are several requests at the same time for successive cycles. If this happens, the channel of the priority circuit having the shortest signal transit time due to manufacturing differences in circuit components allows the same requesting port to be successively served to the exclusion of other ports requesting service at the same time. Service to all the requesting ports is thus unevenly distributed when there are simultaneous requests on successive cycles.